Collections in Cryptology - Silks Key mechanisms in computation... Polyalphabetic keys and one-time-silks meant to be hidden in the lining of a jacket, etc. (A): British WW2 SOE (Special Operations Executive) silk table of 26 mixed alphabets. A key-word would be sent secretly, perhaps hidden in a radio broadcast or a crossword puzzle, which would indicate the order in which the alphabets would be used. If, for instance, the keyword was "PHOENIX," one would use alphabets P, H, O, E, N, I, X in sequence for each letter and repeat the keyword as often as necessary. Assuming that cleartext is given in the black upper-case letters and ciphertext in the red lower-case letters, using the keyword "PHOENIX" we would enclode the cleartext "attack at dawn" as "zeaainxqotfl." Click on the image for an enlargement. John Brunner describes this as "a British One-Time-Pad conversion chart" (Brunner, OSS WEAPONS 1994, p. 205). SRL. No.N.73 (B): British WW2 SOE (Special Operations Executive) silk keys for one month Click on the image for an enlargement. Assuming that a new silk was issued every month, eight five-digit key groups are given for each day of the month. Assume the columns represent the hours in an eight-hour shift during which the message is sent or received, there being three such shifts in a day. Assume the five-digit groups are Vernam-like additive keys, to be repeated for the length of the "clear-text." Past keys could be cut from the sheet and destroyed for security. 1574 (C) British WW2 SOE (Special Operations Executive) "Home to Outstation" silk keys Click on the image for an enlargement. A series of numeric five-digit key groups in two large columns followed by a five-character designator in the third column at the right. John Brunner describes this as "a key for double transposition encoding" (Brunner, OSS WEAPONS 1994, p. 167).